Network Working Group T. Killalea
Request for Comments: 3013 neart.org
BCP: 46 November 2000
Category: Best Current Practice
Recommended Internet Service Provider Security Services and Procedures
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
The purpose of this document is to express what the engineering
community as represented by the IETF expects of Internet Service
Providers (ISPs) with respect to security.
It is not the intent of this document to define a set of requirements
that would be appropriate for all ISPs, but rather to raise awareness
among ISPs of the community's expectations, and to provide the
community with a framework for discussion of security expectations
with current and prospective service providers.
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RFC 3013 Recommended ISP Security November 2000
In this document we define ISPs to include organisations in the
business of providing Internet connectivity or other Internet
services including but not restricted to web hosting services,
content providers and e-mail services. We do not include in our
definition of an ISP organisations providing those services for their
own purposes.
This document is offered as a set of recommendations to ISPs
regarding what security and attack management arrangements should be
supported, and as advice to users regarding what they should expect
from a high quality service provider. It is in no sense normative in
its own right. In time it is likely to become dated, and other
expectations may arise. However, it does represent a snapshot of the
recommendations of a set of professionals in the field at a given
point in the development of the Internet and its technology.
1.1 Conventions Used in this Document
The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
and "MAY" in this document are to be interpreted as described in "Key
words for use in RFCs to Indicate Requirement Levels" [RFC2119].
2 Communication
The community's most significant security-related expectations of
ISPs relate to the availability of communication channels for dealing
with security incidents.
2.1 Contact Information
ISPs SHOULD adhere to [RFC2142], which defines the mailbox SECURITY
for network security issues, ABUSE for issues relating to
inappropriate public behaviour and NOC for issues relating to network
infrastructure. It also lists additional mailboxes that are defined
for receiving queries and reports relating to specific services.
ISPs may consider using common URLs for expanded details on the above
(e.g., http://www.ISP-name-here.net/security/).
In addition, ISPs have a duty to make sure that their contact
information, in Whois, in routing registries [RFC1786] or in any
other repository, is complete, accurate and reachable.
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RFC 3013 Recommended ISP Security November 20002.2 Information Sharing
ISPs SHOULD have clear policies and procedures on the sharing of
information about a security incident with their customers, with
other ISPs, with Incident Response Teams, with law enforcement or
with the press and general public.
ISPs should have processes in place to deal with security incidents
that traverse the boundaries between them and other ISPs.
2.3 Secure Channels
ISPs SHOULD be able to conduct such communication over a secure
channel. Note, however, that in some jurisdictions secure channels
might not be permitted.
2.4 Notification of Vulnerabilities and Reporting of Incidents
ISPs SHOULD be proactive in notifying customers of security
vulnerabilities in the services they provide. In addition, as new
vulnerabilities in systems and software are discovered they should
indicate whether their services are threatened by these risks.
When security incidents occur that affect components of an ISP's
infrastructure the ISP should promptly report to their customers
- who is coordinating response to the incident
- the vulnerability
- how service was affected
- what is being done to respond to the incident
- whether customer data may have been compromised
- what is being done to eliminate the vulnerability
- the expected schedule for response, assuming it can be
predicted
Many ISPs have established procedures for notifying customers of
outages and service degradation. It is reasonable for the ISP to use
these channels for reporting security-related incidents. In such
cases, the customer's security point of contact might not be the
person notified. Rather, the normal point of contact will receive
the report. Customers should be aware of this and make sure to route
such notifications appropriately.
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RFC 3013 Recommended ISP Security November 20002.5 Incident Response and Computer Security Incident Response Teams
(CSIRTs)
A Computer Security Incident Response Team (CSIRT) is a team that
performs, coordinates, and supports the response to security
incidents that involve sites within a defined constituency. The
Internet community's expectations of CSIRTs are described in
"Expectations for Computer Security Incident Response" [RFC2350].
Whether or not an ISP has a CSIRT, they should have a well-advertised
way to receive and handle reported incidents from their customers.
In addition, they should clearly document their capability to respond
to reported incidents, and should indicate if there is any CSIRT
whose constituency would include the customer and to whom incidents
could be reported.
Some ISPs have CSIRTs. However it should not be assumed that either
the ISP's connectivity customers or a site being attacked by a
customer of that ISP can automatically avail themselves of the
services of the ISP's CSIRT. ISP CSIRTs are frequently provided as
an added-cost service, with the team defining as their constituency
only those who specifically subscribe to (and perhaps pay for)
Incident Response services.
Thus it's important for ISPs to publish what incident response and
security resources they make available to customers, so that the
customers can define their incident response escalation chain BEFORE
an incident occurs.
Customers should find out whether their ISP has a CSIRT, and if so
what the charter, policies and services of that team are. This
information is best expressed using the CSIRT template as shown in
Appendix D of "Expectations for Computer Security Incident Response"
[RFC2350].
3 Appropriate Use Policy
Every ISP SHOULD have an Appropriate Use Policy (AUP).
Whenever an ISP contracts with a customer to provide connectivity to
the Internet that contract should be governed by an AUP. The AUP
should be reviewed each time the contract is up for renewal, and in
addition the ISP should proactively notify customers as policies are
updated.
An AUP should clearly identify what customers shall and shall not do
on the various components of a system or network, including the type
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RFC 3013 Recommended ISP Security November 2000
of traffic allowed on the networks. The AUP should be as explicit as
possible to avoid ambiguity or misunderstanding. For example, an AUP
might prohibit IP spoofing.
3.1 Announcement of Policy
In addition to communicating their AUP to their customers ISPs should
publish their policy in a public place such as their web site so that
the community can be aware of what the ISP considers appropriate and
can know what action to expect in the event of inappropriate
behaviour.
3.2 Sanctions
An AUP should be clear in stating what sanctions will be enforced in
the event of inappropriate behaviour.
3.3 Data Protection
Many jurisdictions have Data Protection Legislation. Where such
legislation applies, ISPs should consider the personal data they hold
and, if necessary, register themselves as Data Controllers and be
prepared to only use the data in accordance with the terms of the
legislation. Given the global nature of the Internet ISPs that are
located where no such legislation exists should at least familiarise
themselves with the idea of Data Protection by reading a typical Data
Protection Act (e.g., [DPR1998]).
4 Network Infrastructure
ISPs are responsible for managing the network infrastructure of the
Internet in such a way that it is
- reasonably resistant to known security vulnerabilities
- not easily hijacked by attackers for use in subsequent attacks
4.1 Registry Data Maintenance
ISPs are commonly responsible for maintaining the data that is stored
in global repositories such as the Internet Routing Registry (IRR)
and the APNIC, ARIN and RIPE databases. Updates to this data should
only be possible using strong authentication.
ISPs should publicly register the address space that they assign to
their customers so that there is more specific contact information
for the delegated space.
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RFC 3013 Recommended ISP Security November 20004.2 Routing Infrastructure
An ISP's ability to route traffic to the correct destination may
depend on routing policy as configured in routing registries
[RFC1786]. If so, and if the registry supports it, they should
ensure that the registry information that they maintain can only be
updated using strong authentication, and that the authority to make
updates is appropriately restricted.
Due care should also be taken in determining in whose routing
announcements you place greater trust when a choice of routes are
available to a destination. In the past bogus announcements have
resulted in traffic being 'black holed', or worse, hijacked.
BGP authentication [RFC2385] SHOULD be used with routing peers.
4.3 Ingress Filtering on Source Address
The direction of such filtering is from the edge site (customer) to
the Internet.
Attackers frequently cover their tracks by using forged source
addresses. To divert attention from their own site the source
address they choose will generally be from an innocent remote site or
indeed from those addresses that are allocated for private Internets
[RFC1918]. In addition, forged source addresses are frequently used
in spoof-based attacks in order to exploit a trust relationship
between hosts.
To reduce the incidence of attacks that rely on forged source
addresses ISPs should do the following. At the boundary router with
each of their customers they should proactively filter all traffic
coming from the customer that has a source address of something other
than the addresses that have been assigned to that customer. For a
more detailed discussion of this topic see [RFC2827].
There are (rare) circumstances where ingress filtering is not
currently possible, for example on large aggregation routers that
cannot take the additional load of applying packet filters. In
addition, such filtering can cause difficulty for mobile users.
Hence, while the use of this technique to prevent spoofing is
strongly encouraged, it may not always be feasible.
In these rare cases where ingress filtering at the interface between
the customer and the ISP is not possible, the customer should be
encouraged to implement ingress filtering within their networks. In
general filtering should be done as close to the actual hosts as
possible.
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RFC 3013 Recommended ISP Security November 20004.4 Egress Filtering on Source Address
The direction of such filtering is from the Internet to the edge site
(customer).
There are many applications in widespread use on the Internet today
that grant trust to other hosts based only on ip address (e.g., the
Berkeley 'r' commands). These are susceptible to IP spoofing, as
described in [CA-95.01.IP.spoofing]. In addition, there are
vulnerabilities that depend on the misuse of supposedly local
addresses, such as 'land' as described in [CA-97.28.Teardrop_Land].
To reduce the exposure of their customers to attacks that rely on
forged source addresses ISPs should do the following. At the
boundary router with each of their customers they should proactively
filter all traffic going to the customer that has a source address of
any of the addresses that have been assigned to that customer.
The circumstances described in 4.3 in which ingress filtering isn't
feasible apply similarly to egress filtering.
4.5 Route Filtering
Excessive routing updates can be leveraged by an attacker as a base
load on which to build a Denial of Service attack. At the very least
they will result in performance degradation.
ISPs should filter the routing announcements they hear, for example
to ignore routes to addresses allocated for private Internets, to
avoid bogus routes and to implement "BGP Route Flap Dampening"
[RFC2439] and aggregation policy.
ISPs should implement techniques that reduce the risk of putting
excessive load on routing in other parts of the network. These
include 'nailed up' routes, aggressive aggregation and route
dampening, all of which lower the impact on others when your internal
routing changes in a way that isn't relevant to them.
4.6 Directed Broadcast
The IP protocol allows for directed broadcast, the sending of a
packet across the network to be broadcast on to a specific subnet.
Very few practical uses for this feature exist, but several different
security attacks (primarily Denial of Service attacks making use of
the packet multiplication effect of the broadcast) use it.
Therefore, routers connected to a broadcast medium MUST NOT be
configured to allow directed broadcasts onto that medium [RFC2644].
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RFC 3013 Recommended ISP Security November 20005 Systems Infrastructure
The way an ISP manages their systems is crucial to the security and
reliability of their network. A breach of their systems may
minimally lead to degraded performance or functionality, but could
lead to loss of data or the risk of traffic being eavesdropped (thus
leading to 'man-in-the-middle' attacks).
It's widely accepted that it's easier to build secure systems if
different services (such as mail, news and web-hosting) are kept on
separate systems.
5.1 System Management
All systems that perform critical ISP functions such as mail, news
and web-hosting, should be restricted such that access to them is
only available to the administrators of those services. That access
should be granted only following strong authentication, and should
take place over an encrypted link. Only the ports on which those
services listen should be reachable from outside of the ISP's systems
networks.
ISPs should stay up to date for more secure methods of providing
services as they become available (e.g., IMAP/POP AUTHorize Extension
for Simple Challenge/Response, [RFC2195]).
5.2 No Systems on Transit Networks
Systems should not be attached to transit network segments.
5.3 Open Mail Relay
ISPs should take active steps to prevent their mail infrastructure
from being used by 'spammers' to inject Unsolicited Bulk E-mail (UBE)
while hiding the sender's identity [RFC2505]. While not all
preventive steps are appropriate for every site, the most effective
site-appropriate methods should be used.
ISPs should also strongly encourage their customers to take the
necessary steps to prevent this activity on their own systems.
5.4 Message Submission
Message submissions should be authenticated using the AUTH SMTP
service extension as described in the "SMTP Service Extension for
Authentication" [RFC2554].
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RFC 3013 Recommended ISP Security November 2000
SMTP AUTH is preferred over IP address-based submission restrictions
in that it gives the ISP's customers the flexibility of being able to
submit mail even when not connected through the ISP's network (for
example, while at work), is more resistant to spoofing, and can be
upgraded to newer authentication mechanisms as they become available.
In addition, to facilitate the enforcement of security policy, it is
strongly recommended that messages be submitted using the MAIL SUBMIT
port (587) as discussed in "Message Submission" [RFC2476], rather
than through the SMTP port (25). In this way the SMTP port (25) can
be restricted to local delivery only.
The reason for this is to be able to differentiate between inbound
local delivery and relay (i.e., allow customers to send email via the
ISP's SMTP service to arbitrary receivers on the Internet). Non-
authenticated SMTP should only be allowed for local delivery.
As more and more mail clients support both SMTP AUTH and the message
submission port (either explicitly or by configuring the SMTP port),
ISPs may find it useful to require that customers submit messages
using both the submission port and SMTP AUTH; permitting only inbound
mail on port 25.
These measures (SMTP AUTH and the submission port) not only protect
the ISP from serving as a UBE injection point via third-party relay,
but also help in tracking accountability for message submission in
the case where a customer sends UBE.
6 References
[CA-95.01.IP.spoofing] "IP Spoofing Attacks and Hijacked Terminal
Connections",
ftp://info.cert.org/pub/cert_advisories/
[CA-97.28.Teardrop_Land] "IP Denial-of-Service Attacks",
ftp://info.cert.org/pub/cert_advisories/
[DPR1998] The UK "Data Protection Act 1998 (c. 29)",
http://www.hmso.gov.uk/acts/acts1998/19980029.htm
[RFC1786] Bates, T., Gerich, E., Joncheray, L.,
Jouanigot, J., Karrenberg, D., Terpstra, M.
and J. Yu, "Representation of IP Routing
Policies in a Routing Registry (ripe-81++)",
RFC 1786, March 1995.
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RFC 3013 Recommended ISP Security November 200010 Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
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Acknowledgement
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Internet Society.
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